package csm.common.validator;



import java.io.Serializable;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * <p>Perform email validations.</p>
 * <p>
 * This class is a Singleton; you can retrieve the instance via the getInstance() method.
 * </p>
 * <p>
 * Based on a script by <a href="mailto:stamhankar@hotmail.com">Sandeep V. Tamhankar</a>
 * http://javascript.internet.com
 * </p>
 * <p>
 * This implementation is not guaranteed to catch all possible errors in an email address.
 * For example, an address like nobody@noplace.somedog will pass validator, even though there
 * is no TLD "somedog"
 * </p>.
 *
 * @version $Revision$ $Date$
 * @since Validator 1.4
 */
public class EmailValidator implements Serializable {

    /**
     * Auto-generated serial version UID.
     */
    private static final long           serialVersionUID    = 3799186064442277754L;
    private static final String         SPECIAL_CHARS       = "\\p{Cntrl}\\(\\)<>@,;:'\\\\\\\"\\.\\[\\]";
    private static final String         VALID_CHARS         = "[^\\s" + SPECIAL_CHARS + "]";
    private static final String         QUOTED_USER         = "(\"[^\"]*\")";
    private static final String         WORD                = "((" + VALID_CHARS + "|')+|" + QUOTED_USER + ")";

    private static final String         LEGAL_ASCII_REGEX   = "^\\p{ASCII}+$";
    private static final String         EMAIL_REGEX         = "^\\s*?(.+)@(.+?)\\s*$";
    private static final String         IP_DOMAIN_REGEX     = "^\\[(.*)\\]$";
    private static final String         USER_REGEX          = "^\\s*" + WORD + "(\\." + WORD + ")*$";

    private static final Pattern        MATCH_ASCII_PATTERN = Pattern.compile(LEGAL_ASCII_REGEX);
    private static final Pattern        EMAIL_PATTERN       = Pattern.compile(EMAIL_REGEX);
    private static final Pattern        IP_DOMAIN_PATTERN   = Pattern.compile(IP_DOMAIN_REGEX);
    private static final Pattern        USER_PATTERN        = Pattern.compile(USER_REGEX);

    /**
     * Singleton instance of this class.
     */
    private static final EmailValidator EMAIL_VALIDATOR = new EmailValidator();

    /**
     * Returns the Singleton instance of this validator.
     *
     * @return singleton instance of this validator.
     */
    public static EmailValidator getInstance() {
        return EMAIL_VALIDATOR;
    }

    /**
     * Protected constructor for subclasses to use.
     */
    protected EmailValidator() {
        super();
    }

    /**
     * <p>Checks if a field has a valid e-mail address.</p>
     *
     * @param email The value validation is being performed on.  A <code>null</code>
     *              value is considered invalid.
     * @return true if the email address is valid.
     */
    public boolean isValid(String email) {
        if (email == null) {
            return false;
        }

        Matcher asciiMatcher = MATCH_ASCII_PATTERN.matcher(email);
        if (!asciiMatcher.matches()) {
            return false;
        }

        // Check the whole email address structure
        Matcher emailMatcher = EMAIL_PATTERN.matcher(email);
        if (!emailMatcher.matches()) {
            return false;
        }

        if (email.endsWith(".")) {
            return false;
        }

        if (!isValidUser(emailMatcher.group(1))) {
            return false;
        }

        return isValidDomain(emailMatcher.group(2));
    }

    /**
     * Returns true if the domain component of an email address is valid.
     *
     * @param domain being validated.
     * @return true if the email address's domain is valid.
     */
    protected boolean isValidDomain(String domain) {
        // see if domain is an IP address in brackets
        Matcher ipDomainMatcher = IP_DOMAIN_PATTERN.matcher(domain);

        if (ipDomainMatcher.matches()) {
            InetAddressValidator inetAddressValidator =
                    InetAddressValidator.getInstance();
            return inetAddressValidator.isValid(ipDomainMatcher.group(1));
        } else {
            // Domain is symbolic name
            DomainValidator domainValidator =
                    DomainValidator.getInstance();
            return domainValidator.isValid(domain);
        }
    }

    /**
     * Returns true if the user component of an email address is valid.
     *
     * @param user being validated
     * @return true if the user name is valid.
     */
    protected boolean isValidUser(String user) {
        return USER_PATTERN.matcher(user).matches();
    }

}
